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FILE COPY PUBLIC H?ALTH SERVIAS ,oP��%` SAN JOAQUIN COUNTY 2r ENVIRONMENTAL HEALTH DIVISION . Karen Furst, M.D., M.P.H., Health Officer :iFo.RN,P 304 East Weber Avenue, Third Floor • Stockton, CA 95202 209/468-3420 APR 17 2000 KAREN PETRYNA C/O EQUIVA LLC PO BOX 6249 CARSON CA 90749-6249 RE: TEXACO STATION SITE CODE: 1055 440 W CHARTER WAY STOCKTON CA San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has recently reviewed the last four quarters of groundwater monitoring reports (QMER's), the second generation tank pull report and the most recent workplan associated with the site referenced above. Although groundwater monitoring is continuing,the plume is undefined.Data from monitor wells at this facility fail to characterize the vertical and lateral extent of groundwater contaminant distribution. Concentrations of fuel hydrocarbons (TPHg,Benzene and MTBE) in down gradient monitor wells MW-9, 10, 11 and 15 are significantly above primary and secondary water quality standards(MCL's&Taste and Odor Thresholds). On May 26, 1999 PHS/EHD issued a written directive including the following site-specific requirements. "Boreholes shall be completed as monitoring wells with appropriate screen intervals to locate and effectively define the plume (soil and groundwater). At least two boreholes should be continuously cored. Each continuous core borehole should be located near known contaminant source areas (i.e.,former tank cavity). All wells installed and surveyed shall be referenced to an appropriate and designated benchmark. Well screen intervals shall not exceed 20'in total length and should not create a potential vertical conduit. Report the results ofyour investigation to this agency within 30 days of completion of the approved scope of work. You are requested to properly characterize the hydrogeology and groundwater flow conditions in the vicinity of your site. We also request that you evaluate local groundwater flow conditions and establish a site-specific localized flownet that is dependent on geologic conditions and is reflected on geologic cross sections and fence diagrams. Additionally you are required to prepare a rose diagram displaying groundwater gradient intensity and flow direction. The rose diagram shall be updated to show all historic groundwater gradients and flow directions to date and shall be provided for all future monitoring event reports. All plot plan and cross section drawings shall show the location of former and present UST appurtenances. We request that you continue to monitor the groundwater contaminant plumes on a quarterly basis. Additional wells will be required to define the down gradient extent of the plume if the plume continues to migrate or the first set of wells fail to define the plume(s). In the event continued plume migration is identified, or impact to water supply wells is predicted please include recommendations for the installation of additional wells or remediation alternatives in your Quarterly Reports." The workplan and QMER's submitted since May 26, 1999 fail to address these directives. The most recent workplan is proposing only one CPT borehole near SB-3, it is unlikely that one CPT borehole can define the plume and repeated mobilizations are likely to be less cost effective. PHS/EHD now recommends the 1 . A Division of San Joaquin County Health Care Services